1. Field of the Invention
This invention relates to an aqueous dispersion having a solids content of from about 5 to 50% by weight of a copolymer of ethyl acrylate, methacrylic acid, acrylic acid and a polyethylenically unsaturated copolymerizable monomer. The dispersion is suitable for thickening aqueous systems, particularly hydrogen peroxide preparations of the type used as the developer composition for oxidative hair dyes and for hair bleaches.
2. Description of Related Art
It has long been known that alkali-soluble acrylate dispersions may be used for thickening aqueous systems. Dispersions having a solids content of from 25 to 50% by weight of a copolymer comprising at least 10% by weight of an acrylic acid lower alkyl ester, 25 to 70% by weight methacrylic acid and, optionally, 0 to 40% by weight of another monoethylenically unsaturated co-monomer are described, for example, in Great Britian Pat. No. 870,994. German Application No. 1,164,095 describes copolymers of 50 to 75% by weight ethyl acrylate, 25 to 35% by weight acrylic acid and 0 to 25% by weight of other co-monomers.
These publications indicate that the molecular weight of the copolymers and hence their thickening effect can be increased by the addition of a polyethylenically unsaturated copolymerizable cross-linking co-monomer. According to Great Britian No. 870,994, a cross-linking co-monomer content of from about 0.1 to 0.8% by weight and preferably from about 0.15 to 0.3% by weight of the copolymer leads to particularly favorable acrylate copolymers.
However, these known copolymer dispersions do not completely satisfy the stringent demands needed for effective thickening, particularly when the dispersions are used in cosmetic preparations. Neutralized dispersions of these copolymers, for example, often show a marked tendency towards legging, thus making them unsuitable for cosmetic applications due to the greasy feel they impart to the skin. Additionally, some dispersions show only moderate thickening power; while with other dispersions, the viscosities of the thickened preparations are extremely sensitive to other ingredients in the ultimate formation, i.e., the viscosity of the thickened preparations may be either severely reduced or possibly increased into the gel range by certain constituents of the formulation, e.g., electrolytes. With these prior art dispersions, some preparations also show an excessive and unfavorable viscosity dependence on the concentration of the thickener.
Particularly stringent demands are made of alkali-soluble acrylate copolymer dispersions used for thickening hydrogen peroxide preparations. Preparations of this type are commonly employed as developer compositions for oxidative hair dyes and for hair bleaches. The mildly acidic preparations are mixed with an alkaline dye cream just before application to the hair to form an alkaline dye preparation. Since this destroys the consistency of the cream, a thickener dispersion is included in the developer preparation in order to achieve a mixture viscosity suitable for applying the alkaline dye preparation to hair after the two components have been combined.
Even though formulations of various oxidative hair dyeing preparations may differ considerably, developer compositions--for the same dosage--should always ensure that mixtures of the dye cream and the developer composition have a proper consistency for the end use. This result is possible only if the thickener responsible for enhancing consistency is particularly effective and immune to troublesome influences.
The same can be said about hair bleaches, which also are formulated as two-component products consisting of a mildly acidic hydrogen peroxide preparation and an alkaline bleaching cream. Again, these components are mixed together before application. The compositions of the two components and their proportions in the final mixture are such that the hair bleach is alkaline after the two components have been combined. The hydrogen peroxide preparation should contain a thickener dispersion which adjusts the viscosity of the blended hair bleach to a value suitable for application to hair.